This research will be done primarily in Hungary as an extension of NIH Grant #R01 DC 04263. The goal of the proposed research is to characterize the processes leading to the perception of distinct sound sources. Our previous results (see Preliminary Results) established that a large part of auditory organization occurs preperceptually. The aim of the proposed research is to determine whether the perceived segregation of sources is the result of a single process or whether auditory organization goes through several distinct phases before reaching perception. Finding a preperceptual organization that differs from the perceived organization would support the notion of a multi-stage process. To reach this goal we will use the high temporal resolution of event-related potentials (ERPs) in conjunction with behavioral methods to compare the outcome of stimulus-driven auditory processes with the perception resulting from attentive processing of the same sounds, across various experimental conditions. This will allow us to evaluate the processing stages of auditory organization and determine how much of the perceptual organization is strictly stimulus driven and how much can he altered by attentional processes. The FIRCA proposal will expand on Specific Aim 2 of the parent grant ("the interplay between attention and stimulus-driven processes in perception"). Three experiments are proposed to address this aim. Experiment 1 will determine to what extent perceptual sound organization corresponds to an assessable preperceptual organization. Experiment 2 will investigate what stage of auditory processing are multiple cues (differences between two sets of sounds in two or more auditory features) summed in segregating sound sources. Experiment 3 will test whether alternative sound organizations (i.e., the integrated and the segregated organizations) of the same two sets of sounds can exist in parallel at an assessable preperceptual processing stage.